This invention relates in general to trailers and more particularly to a hitch assembly for coupling a trailer to a tow vehicle.
Automobiles and pick-up trucks have long been used to tow trailers, and in the typical combination the trailer is connected to the tow vehicle through a ball and socket coupling located at the rear of the tow vehicle. More specifically, the tow vehicle is fitted with a hitch ball which projects upwardly in the region of the rear bumper for that vehicle, while the trailer at the end of its tongue has a socket which fits over and closes around the hitch ball, thereby securing the trailer to the tow vehicle such that the trailer may turn relative to the tow vehicle, rock forwardly and rearwardly with respect to the tow vehicle, and also rock left and right with respect to the tow vehicle, or in other words undergo a universal pivoting movement.
The offset of the hitch from the rear axle of the tow vehicle detracts from the overall stability of the combination, particularly at higher speeds, for it enables wind induced forces to cause a swaying motion known as fishtailing. The wind may amount to nothing more than a simple surface wind of the type often present, particularly in the plains states, or it may be gusts of the type experienced during storms. The wind may also be generated by a large over-the-road truck traveling at high speed, for such a vehicle will displace a considerable amount of air and create turbulence that affects any other vehicle which happens to be along side of it. Inertial forces created by uneven road surfaces may also produce fishtailing. Typical of this type of road surface is a shoulder onto which the wheel on one side of a trailer may run. As the trailer wheel climbs back onto the pavement, the trailer experiences a sudden jolt which may induce fishtailing.
Irrespective of its source, fishtailing is dangerous for it may cause the driver of the tow vehicle to lose control of his vehicle. Moreover, fishtailing imposes severe stresses on the trailer hitch and the frame components to which it is attached, and may bend or fracture them. Fishtailing likewise imposes severe demands on the suspension system of the tow vehicle, and may cause components such as shock absorbers, bushings and springs to experience excessive wear or to fail.
While large over-the-road tractor-trailer combinations would, because of their size, seem more susceptible to fishtailing, they are not, and this to a large measure derives from the fact that the pivot axis for the trailer is set generally over the rear axle of the tractor. In vehicles with tandem rear axles, the pivot mechanism or fifth wheel as it is called is often located over the space between the two axles. In any event, tractor-trailer combinations do not pivot substantially behind the rear axle or axles of the tractor, and therefore these combinations possess good stability at high speeds.
Devices are currently available for reducing swaying and fishtailing, but these have the effect of stiffening the pivot joints at which they are used. They are not very effective, and they impose substantial stresses on the vehicular components to which they are attached, particularly when turns are negotiated. Heretofore, attempts have been made to stabilize trailers by employing converting linkages in the hitch mechanisms, with these linkages having the effect of displacing the effective pivot axis for the hitch mechanism forwardly, even though the hitch mechanism is not in any sense located in the region to which the axis is displaced. U.S. Pat. No. 4,019,754 shows such a linkage arrangement. Hitch mechanisms of this type cannot accommodate sharp turns of the type one may encounter in urban areas or in attempting to park a trailer in a confined parking place.